This invention relates to aircraft escape systems, in particular to aircraft ejection seats.
Ejection seats in high performance military aircraft must be capable of safely removing the pilot or other occupant from the stricken aircraft across a wide variety of aircraft speed regimes, altitudes and aircraft attitudes. The most difficult ejection occurs when the aircraft is at low altitude and at an inverted or other non-upright orientation. Approximately 50% of the United States Air Force fighter aircraft ejection fatalities occur due to insufficient altitude at the time of ejection. Without sufficient altitude, the occupant's recovery parachute cannot fully deploy to bring the occupant safely to the ground.
It has long been recognized that an aircraft ejection seat having the capability of assuming an upright orientation irrespective of the aircraft attitude and thereafter gaining sufficient altitude for a safe parachute deployment would be desirable for reducing ejection fatalities. U.S. Pat. No. 4,216,928 to Hooper, et al. discloses a microwave radiometric attitude reference system that uses microwave radiometry to sense the orientation of the ejection seat. Pitch and roll of the ejection seat are controlled by a linear pitch servo actuator and a linear roll servo actuator that move a single gimbal-mounted rocket motor.
U.S. Pat. No. 4,303,212 to Stone, et al. discloses an aircraft ejection seat that includes an attitude control processor, which processes signals from three attitude sensors and uses those signals to control a pair of servo valves. The servo valves actuate a linear pitch servo and a linear roll servo that act on a gimbal-mounted spherical rocket motor.
U.S. Pat. No. 4,721,273 to Trikha discloses an aircraft ejection seat in which the main thrusters have steerable nozzles for the purpose of changing the direction of the thrust axis. The ejection seat also includes a pair of fixed, opposed roll control thrusters and a pair of fixed pitch control thrusters that operate together to maintain the ejection seat in an upright orientation.
U.S. Pat. No. 4,236,687 discloses an aircraft ejection seating having pitch, roll and yaw control. The ejection seat includes two spherical gimbal-mounted rocket motors each of which is acted on by two linear hydraulic actuators. Pitch and roll are controlled by varying the position of the two rocket motors in unison. Yaw control is accomplished by positioning the rocket motors so that the thrust vectors are not parallel, which produces a torque about the yaw axis of the ejection seat.
Although linear actuators acting on large spherical rocket motors could theoretically accomplish the desired pitch, roll and yaw control, in practice the large moment of inertia of the spherical rocket motor necessitates very large and powerful linear actuators to move the rocket motors to maintain stable flight. Large powerful hydro-pneumatic actuators, in turn, are heavy and require substantial power to operate, which leads to a heavier ejection seat which requires a larger rocket motor, necessitating more powerful hydro-pneumatic actuators and so on. Accordingly, what is needed is an ejection seat with pitch, roll and yaw control that incorporates low moment of inertia rockets and actuators in order to meet the size and weight constraints as well as reaction times necessary for the ejection seat to achieve upright stable flight.